not sure if this belongs in this section but i'll try. i gues this is A STUPID question but if i bore out my block for 84mm pistons would i have to bring the head to get machined to match. im thinking i do to make good combustion but i could be wrong. thanks for the help

 

As long as your pistons don't come out of the bore at all at TDC it will be fine.

 

you dont have to. but some people do it anyway. remember, opening up the combustion chambers will have an effect on static compression.